The Universal Mobile Telecommunication System (UMTS) standardized in the 3rd Generation Partnership Project (3GPP) has been known as a third-generation radio communication system for implementing packet communication using radio access technology.
FIG. 1 shows the configuration of a conventional radio communication system including a UMTS network. As shown in FIG. 1, base stations BS, a radio network controller RNC, a subscriber node SGSN (Serving GPRS Support Node), and a gateway node GGSN (Gateway GPRS Support Node) are disposed in the UMTS network. The UMTS network is connected to a packet communication network such as the Internet. Communication terminals TE such as personal computers (PC) can be connected to the UMTS network via mobile stations MS.
FIG. 2(a) shows a protocol stack in the conventional radio communication system. FIG. 2(b) shows the configuration of a Radio Link Control (RLC) connection and GPRS Tunneling Protocol (GTP) connections established in the conventional radio communication system.
As shown in FIG. 2(a), in the conventional radio communication system, an RLC connection based on the RLC protocol is established between the mobile station MS and the radio network controller RNC.
A GTP connection is established between the radio network controller RNC and the subscriber node SGSN. A GTP connection based on the GTP protocol is established between the subscriber node SGSN and the gateway node GGSN.
Here, in the radio network controller RNC, the RLC connection established with the mobile station MS is associated one-to-one with the GTP connection established with the subscriber node SGSN.
In the subscriber node SGSN, the GTP connection established with the radio network controller RNC is associated one-to-one with the GTP connection established with the gateway node GGSN.
Radio communication systems generally need to handle communications which require various qualities of service (QoS), from communications which require real time such as voice communications and video communications, to communications which permit some delay such as e-mails.
For this, it is known to perform QoS control in a transport technology such as the Asynchronous Transfer Mode (ATM) technology or the IP technology, so as to meet QoS requirements such as an allowable transmission delay and an allowable packet loss in each communication.
In the ATM technology, for example, various traffic management techniques are defined, so that functions of dealing with various QoS requirements, from guaranteed-bandwidth services to best-effort services, can be used. In the IP technology, QoS control functions such as Differentiated Services and Integrated Services can be used.
However, when a plurality of communications are multiplexed to an RLC connection as shown in FIG. 2(b), that is, when a plurality of data packets are multiplexed and loaded into RLC-PDUs (Protocol Data Units), the data packets are handled as having the same QoS requirement at an ATM connection (or at an IP tunneling connection, an MPLS connection or the like), and there occurs the problem that QoS control cannot be performed on each communication.
To solve this problem, it has been conceived that, as shown in FIG. 2(C), in the conventional radio communication system, the mobile station MS creates multiple “Packet Data Protocol (PDP) contexts” for data packets having different QoS requirements, according to communication destinations and the QoS requirements, and establishes multiple RLC connections for the created PDP contexts.
A PDP context is a collection of information set for the subscriber node SGSN, the gateway node GGSN and so on before communication. The PDP context includes communication status information, information on QoS requirements required in a communication, communication destination information and so on.
In the conventional radio communication system, the base station BS and the radio network controller RNC perform synchronous control at the start of communication, for determining a transmission timing of an MAC-PDU from the radio network controller RNC to the base station BS.
In a soft handover where a mobile station MS performs communications through different base stations BS at a time, the synchronous control allows the different base stations BS to transmit an MAC-PDU to the mobile station MS simultaneously using the W-CDMA technology.
Here, the timing for the base stations BS to transmit the MAC-PDU transmitted from the radio network controller RNC to the mobile station MS is determined in view of a transmission delay between the base stations BS and the radio network controller RNC, a wait time due to QoS control and so on.
The base stations BS are configured to refer to a sequence number given to a Frame Protocol (FP) frame transmitted from the radio network controller RNC, and transmit an MAC-PDU included in the FP frame of an appropriate sequence number at a transmission timing determined as described above.
However, the conventional radio communication system has the problem that a mobile station MS needs to establish a plurality of RLC connections for data packets with different QoS requirements even for communication with the same communication destination, and must have the capability of establishing a plurality of RLC connections.
Also, the conventional radio communication system has the problem that a mobile station MS must perform a path change for all established RLC connections and GTP connections at the same time, when changing a communication path due to a handover, which results in an increased control load and reduced performance.
Also, the conventional radio communication system has the problem that since a wait time for a low-priority MAC-PDU is set long in the base station BS, even when an FP frame including a low-priority MAC-PDU is transferred from the radio network controller RNC to the base station BS with a small delay, the base station BS must wait to transmit the MAC-PDU included in the FP frame until a determined timing.
The present invention has been made in view of the above problems, and has an object of providing a packet communication method, a controller device and a mobile station for being able to reduce the number of RLC connections to be established, to improve performance in radio communication systems.